This equipment item is, for example, an airborne nacelle 100, diagrammatically represented in cross section in FIG. 1. This nacelle comprises a fixed element 110 and a movable element 120 rotating about an axis of rotation 140. The figure also shows two fluid-tight rotation-guiding devices 130a, 130b in a ring configuration which guide the movable element 120 of the nacelle in its rotation about the axis of rotation 140. A portion of one of these rotation-guiding devices is shown in close-up.
There are currently various types of rotation-guiding devices.
Rotation-guiding devices with a dynamic seal, an example of which is shown in FIG. 2, can be cited as an indication. These devices comprise:
a supporting structure comprising a fixed support 11 secured to the fixed element 110 of the equipment item and a movable support 12 secured to the movable element 120 of the equipment item and capable of rotating around the fixed support about an axis of rotation 140,
an interface between the fixed 11 and movable 12 supports which comprises a flexible dynamic seal 1 secured to the fixed support 11 (or the movable support 12), which provides the dynamic seal between these fixed and movable supports. An example of a tight dynamic seal is shown in FIG. 3. It notably comprises:
a bearing face 2 intended to bear on the fixed support 11,
a friction face 3 parallel to the bearing face, intended for the dynamic contact with a friction track 4 linked to the movable support, this friction face usually being less wide than the bearing face,
and a metal spring 5 placed between the bearing face 2, the friction face 3 and an intermediate face 6 joining the bearing face and the friction face, and the function of which is to separate these two faces to ensure that the friction face 3 is brought into contact with the friction track 4 according to a contact force perpendicular to the friction face. This contact force can also be obtained without a spring, by deformation of the dynamic seal.
Referring now to FIG. 2, the interface also comprises a revolving bearing 135 which guides the movable support 11 in its rotation around the fixed support 12 and which comprises a row of balls 13 housed between two raceways formed in an inner ring 131 and an outer ring 132 respectively fixed to the fixed 11 and movable 12 supports of the rotation-guiding device.
In the context, for example, of the design of an airborne nacelle, it is necessary to produce equipment with a reduced bulk and weight, capable of withstanding severe vibratory environments, impacts and pressure and temperature variations, without performance levels being degraded or altered. In the case of an airborne nacelle, the pressure variations between the interior and the exterior of the nacelle can reach 1 bar and the temperature variations are between −55° C. and 80° C. The current seals conventionally made of elastomer have an expansion coefficient such that, when subject to a drop in temperature, they shrink, leading to a reduction, or complete absence, of seal-tightness. When subject to a rise in temperature, they expand, unacceptably increasing the friction force. The performance levels of the current rotation-guiding devices with dynamic seals are inadequate in the stated pressure and temperature variation conditions: their use is limited to temperatures above −20° C.
Some of the rotation-guiding devices currently used to provide better performance use a technology based on ferrofluids to provide the dynamic seal between the fixed and movable parts of the device. However, this technology is costly and exhibits high viscous friction torques at low temperature. This drawback can be compensated by a system for reheating the ferrofluid to the detriment of the cost, the bulk and the complexity of the device. An exemplary ferrofluid rotation-guiding device is represented in FIG. 4. It comprises a movable support 12, a fixed support 11, a bearing 135, a sealing element 1′ formed by an oil film held in place by a magnetic field acting on conductive particles contained within the oil film.